198 
ELEMENTS OE GEOLOGY. 
The Coralline Crag rarely, if ever, attains a thickness of 
thirty feet in any one section. Mr. Prestwich imagines that 
if the beds found at different localities were united in the 
probable order of their succession, they might exceed eighty 
feet in thickness, but Mr. Searles Wood does not believe in 
the possibility of establishing such a chronological succession 
by aid of the organic remains, and questions whether proof 
could be obtained of more than forty feet. I was unable to 
come to any satisfactory opinion on the subject, although at 
Orford, especially at Gedgrave, in the neighborhood of that 
place, I saw many sections in pits, where this crag is cut 
through. These pits are so unconnected, and of such limit¬ 
ed extent, that no continuous section of any length can be 
obtained, so that speculations as to the thickness of the whole 
deposit must be very vague. At the base of the formation 
at Sutton a bed of phosphatic nodules, very similar to that 
before alluded to in the Red Crag, with remains of mamma¬ 
lia, lias been met with. 
Whenever the Red and Coralline Crag occur in the same 
district, the Red Crag lies uppermost; and in some cases, as 
in the section represented in Fig. 126, which I had an oppor- 
Fig. 126. 
Sutton. Shottisham Kamsholt. § 
Section near Woodbridge, in >SufFolk. 
a. Red Crag, h. Coralline Crag. c. London clay. 
tunity of seeing exposed to view in 1839, it is clear that the 
older deposit, or Coralline Crag, J, had suffered denudation, 
before the newer formation, a, was thrown down upon it. At 
D there was not only seen a distinct cliff, eight or ten feet 
high, of Coralline Crag, running in a direction K.E. and S.W., 
against which the Red Crag abuts with its horkontal layers, 
but this cliff occasionally overhangs. The rock composing 
it is drilled everywhere by Pholades^ the holes which they 
perforated having been afterwards filled with sand, and cov¬ 
ered over when the newer beds were thrown down. The 
older formation is shown by its fossils to have accumulated 
ill a deeper sea, and contains none of those littoral forms such 
as the limpet. Patella^ found in the Red Crag. So great an 
amount of denudation could scarcely take place, in such inco¬ 
herent materials, without some of the fossils of the inferior 
beds becoming mixed up with the overlying crag, so that 
considerable difficulty must be occasionally experienced by 
